Casein, the principal protein in milk, can be isolated in various forms fairly easily by insolubilization.
This invention is concerned only with acid casein. The expression "acid casein" is used in its broad sense and covers both traditional acid casein directly obtained by acidifying milk, and acid caseins obtained indirectly, such as for example a re-acidified rennet casein. Acid casein is readily available as a commercial product.
There is interest in solubilizing acid caseins in water without any major difficulties, and in converting acid caseins into a form in which they can be easily stored and transported, i.e., into powder form. Prior to this invention, the redissolution of powdered acid casein in an aqueous medium has required many precautions.
U.S. Pat. No. 4,055,555 to Badertscher et al. teaches that powdered sodium caseinate or a homogeneous solution of caseinate is prepared by providing an aqueous medium which may be pure water or an aqueous solution containing various ingredients, such as salts, sugars, colorants, flavorings, soluble proteins, especially lactalbumin (for example an aqueous medium of whey type), etc. The acid casein is added to the aqueous medium and allowed to age. After ageing, the solubilizing agent is added to provide the desired suspension. If a powder is desired the suspension is dried.
The Badertscher patent teaches an ageing time of at least 10 minutes and preferably 30 minutes, and shows a solubilizing and neutralization time of approximately 2.5 to 3.0 hours. Insoluble clump formations of the casein powder occur in water above 100.degree. F. or in a solution that is too rapidly heated above the same temperature. Thus, the ageing and the neutralization of casein is a temperature-dependent reaction requiring gradual heating, specifically during two critical points of the process.
The first critical point involves the addition of casein to the water. Casein placed in solution hydrates extremely fast. The addition of casein to water above 100.degree. F. causes a reduction in surface area and lumping which in turn yields an exothermic product. Furthermore, tryptophan, which is one of casein's amino acids, is damaged if the temperature of the water exceeds 170.degree. F.
The second critical point occurs during neutralization and involves the addition of sodium hydroxide (NaOH) to the solution. The casein to caseinate conversion occurs when sodium hydroxide (NaOH) is added to the solution. If NaOH is added to water above 100.degree. F., the resulting product will be an unneutralized material trapped in a shell. Thus, prior to the present invention, caseins had to be neutralized in water that was initially in the range of 70.degree. F. to 100.degree. F. After the casein was neutralized in this range for about 30 minutes, the temperature of the solution was gradually increased to approximately 160.degree. F.
The Badertscher patent states that the temperature may be as high as approximately 176.degree. F. in continuous operation, although it is preferably in the range from 68.degree. F. to 158.degree. F. However, the dispersion of casein in water above 100.degree. F. without the presence of a solubilizing agent will yield a useless, insoluble clump of casein powder. Thus, in order to reach these high temperatures, the examples of the Badertscher patent employ an initial dispersion of casein at lower temperatures and then a gradual heating of the solution to obtain the higher temperatures.
Hence, not only is the solubilization and neutralization of casein according to the teaching of the Badertscher patent temperature-dependent, but Badertscher also requires a gradual heating process (see example 1, column 5-6; example 2, column 6; example 3, column 6) in order to obtain usable caseinate. Badertscher states the casein suspension must be "left to age" or "wetted out". This phrase means that addition of the solubilizing agent to the suspension may not be made until the casein in powder form is hydrated throughout.